The invention relates to a method for securing a high-voltage on-board electric grid of a motor vehicle for repair and/or maintenance work on the motor vehicle. The invention also includes a motor vehicle with a high-voltage onboard electric grid and a diagnostic device for such a motor vehicle.
During work on a high-voltage system of a motor vehicle or in close proximity to such a high-voltage system it has to be ensured that this system is free of voltage. For this purpose a voltage disconnection is performed. A first important step hereby is that a connection between a high-voltage battery of the high-voltage system and a high-voltage onboard electric grid for distributing the high-voltage in the motor vehicle is interrupted. For this purpose, usually contactors are provided in the high-voltage battery, which are opened by a control device. Opening of the contactors then blocks the energy supply of the high-voltage battery into the high-voltage onboard electric grid. Subsequently the electric voltage in the high-voltage onboard electric grid can then be manually measured by means of a voltage tester or also automatically by means of a testing device fixedly installed in the motor vehicle, i.e., a control device. Depending on the circumstances a residual voltage, for example stored by capacitances in the high-voltage onboard electric grid, may have to be eliminated. Subsequently a person may then perform the necessary work on the motor vehicle.
During this work it has to be ensured that electric voltage is not inadvertently built up again in the high-voltage onboard electric grid. For this purpose the professional association requires that certain steps must not be performed after the voltage disconnection has occurred because they may lead to a build-up of electric voltage in the high-voltage onboard electric grid again. For example, one must not insert the charging plug of a vehicle-external charging device into the plug-in shaft of the charging device of the motor vehicle once the voltage disconnection has occurred. In a vehicle type, which additionally has an internal combustion engine to drive an electric generator in the motor vehicle, also the internal combustion engine must not be restarted because this would drive the generator and produce electric voltage. Motor vehicle types with such additional internal combustion engines are also known as plug-in-vehicles or range-extender-vehicles. The described safety measures are usually implemented by a process, i.e., exact instructions have to be followed by persons working on the motor vehicle. This leaves the human as the greatest uncertainty factor during the work because, due to uncoordinated collaboration, a person may inadvertently insert a charging plug while another person for example still works underneath the vehicle.
From DE 10 2010 063 126 A1 and WO 2012 072 308 A2 charging devices with a device for separating a high-voltage battery from an intermediate circuit and for separating current-conducting lines of a charging cable and a monitoring device are known, which is configured to monitor the charging device with regard to a dangerous situation which causes the risk of an electric shock. The device for separation and an additional discharging device are configured to respectively generate a control signal in dependence on the determined dangerous situation.
IN DE 10 2011 104 819 A1 a motor vehicle high-voltage system is described in which in a first high-voltage range after separation from a second high-voltage range is secured against reactivation by a separation device. The securing is accomplished by of switching the battery contactor currentless, setting a blocking bit in a high-voltage component such as an electric motor, deactivating a charging device for the high-voltage system or switching off an electric motor in order to prevent voltage generated by pushing the motor vehicle.
DE 10 2010 052 375 A1 describes a motor vehicle in which a traction battery can be charged via a charging cable, wherein an electric contact of a charging contact element of the energy storage unit is interrupted when the charging cable is not connected with the charging connection element within a defined period of time after turning off the motor vehicle. To accomplish the blocking for example a pin can be inserted motor-driven into a connection socket of the charging device.